1. Technical Field
This invention relates to a read head assembly for sensing recorded data from tracks on moving magnetic media, such as magnetic tape, floppy disks or hard disks, and, more particularly, to a magnetoresistive read head with 4-point sensing.
2. Background Art
Typical magnetoresistive read heads include a magnetoresistive strip which functions as a sensing element. The strip is used to sense the recorded data from the track of the moving magnetic media. The data recorded on a section of the track applies a magnetic field to the strip when the strip is adjacent to the track. Essentially, the strip is a thin layer of a magnetically sensitive material, such as permalloy whose resistance varies under applied magnetic fields. Thus, the data recorded on the media track causes the resistance of the strip to vary. Monitoring the resistance of the strip allows the data to be read.
The resistance of the magnetoresistive strip is measured by forcing a predetermined amount of current through sensing leads and into the stripe. The voltage is then measured across the leads. Any change in voltage indicates a change in the resistance of the portion of the strip between the leads. Accordingly, the track is delimited by the distance between the sensing leads, not the size of the stripe.
These magnetoresistive read heads are subject to an extreme form of "wiggle" or "Barkhausen noise". To stabilize the head and minimize the noise, it is essential to control the domain structure of a magnetoresistive stripe. Ideally, the portion of the magnetoresistive strip which actively senses the recorded data from the track of the magnetic media (i.e. the area between the sensing leads) should be in a single-domain state. However, even if a single-domain state is substantially achieved, a problem arises when the track width is set too narrow.
A narrow track width is important. Recent advances in the art of magnetic data storage have resulted in improved storage densities. Typically, these improved storage densities are achieved by use of higher track densities in which recorded data is stored in tracks narrower than those used previously. The narrower the track, the more data that can be stored on the media. Wide-track magnetoresistive heads are known to have worked very well. However, narrow-track heads needed for improved storage densities have been found to be noisy. The degraded performance is caused, in part, by the current forced through the strip at the same portion of the strip used to sense data on the media. The current affects the domain states of the magnetoresistive material in the portion of the strip between the sensing leads.
FIG. 1 shows a perspective view of the magnetoresistive strip 12 and the sensing leads 14. The forced currents flowing in them are shown by the solid arrows. These forced currents create parasitic fields in the strip which can disrupt the magnetic domains. The direction of the parasitic fields created in the strip 12 are shown by the dashed arrows. As can be seen, depending on the direction of the forced current, one of the leads 14 will always generate a field opposite the intended stripe magnetization which is in one of either direction along the longitudinal axis of the strip 12. The effect of the parasitic field is generally confined to the area immediately surrounding the lead 14. However, since the portion of the magnetoresistive strip 12 used to sense the magnetic media is directly bounded by the lead 14, it will be affected. It is this parasitic field which disrupts the magnetic domains of the strip 12. In a wide track system, the disruption is not as severe because it is localized around the leads 14, leaving much of the area between the leads 14 unaffected. However, as the track width is narrowed, the disruption becomes progressively worse because a larger percentage of the area between the leads 14 is affected.
Accordingly, it is an object of the present invention to provide an apparatus and method for monitoring the resistance of the magnetoresistive strip which does not induce parasitic fields which can disrupt the magnetic domains of the strip material between the sensing leads. This in turn would allow the use of narrow track widths without the noise experienced in current read head assemblies.
In addition, further objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.